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Papers by Alessandro Airoldi

Research paper thumbnail of Chiral-Rib Structures for Morphing Wings

Research paper thumbnail of Design of a Morphing Wing Using a Composite Chiral Structure

Research paper thumbnail of Composites Interlaminar Toughening Techniques by Means of Interleaved Nanofiber Veils: Experimental Evaluation

Research paper thumbnail of Modelling Technique to Optimise Energy Absorption in Helicopter Crashes

Research paper thumbnail of Evaluation of SLS-made PA 12 Under Uniaxial Tensile Test

The morphing structures provide a development in aero field applications and they are being a rea... more The morphing structures provide a development in aero field applications and they are being a realistic imitation of nature over time, bringing good efficiencies in many factors with respect to the conventional methodologies. On the other hand, these structures have some not-well predicted behaviors with new material applications. Polyamide 12 (PA12) is one of these new century materials manufactured by one of unconventional technologies, namely Selective Laser Sintering (SLS). Based on the morphing structures, the hexachiral and hexachiral tessellation morphologies are two of the in-demand researches not only in aero field but also in many other fields. As a sub-field of these researches, out-of-plane and in-plane crashworthiness of the hexachiral morphologies are being a great subject to be examined. Moreover, even there are many researches belong to out-of-plane crashworthiness, solely a limited number of resources for in-plane behavior can be found in literature. As a study case...

Research paper thumbnail of Tecniche di formatura di compositi con fibre vegetali e loro caratterizzazione

Research paper thumbnail of Optimisation of Energy Absorbing Subsystems for Helicopter Vertical Crashes

The experience gained in the last decades on the development of crashworthiness helicopter struct... more The experience gained in the last decades on the development of crashworthiness helicopter structures indicates that occupants’ protection can be achieved integrating different energy absorbing systems in landing gears, subfloor and seats. However, the mutual interactions between these different subsystems must be considered to achieve higher overall performances in case of crash events. This work proposes a numerical approach for the evaluation of the overall undercarriage performance, basing on an hybrid multi-body and finite element approach. A hybrid scheme of the subfloor lay-out is integrated with a multibody model of a crashworthy seat and an anthropomorphic dummy model. The modelling technique has been used to investigate and optimize the effects of local aspects on the overall crashworthy performances of the system such as the subfloor and the seat absorbing devices. Basing on the obtained results, the proposed methodology seems a promising approach to deal with the optimiz...

Research paper thumbnail of Development and Application of Numerical Approaches for Short Fibre Reiforced Ceramics

Topic: Structures and Materials) Ceramic matrix composites (CMC) have been extensively studied si... more Topic: Structures and Materials) Ceramic matrix composites (CMC) have been extensively studied since their discovery in the mid- seventies, particularly those made of silicon carbide (SiC) matrix with discontinuous carbon reinforcement. These materials are obtained by reinforcing a SiC matrix with bundles each made of hundreds or thousands of fibers. They present remarkably high toughness compared to traditional ceramics and have the potential of being used as structural materials in different fields, at temperatures up to about 1500°C. Present or potential applications include braking systems for aeromobiles and motor vehicles, spacecrafts, advanced engines, stationary gas turbines for power/steam co-generation, heat exchangers, heat treatment furnaces and components for nuclear reactors. A critical aspect is the necessity to evaluate, in terms of stiffness and strength, the expected material performance of structural elements made of CMC. In fact, traditional micromechanical appro...

Research paper thumbnail of Numerical Analyses of Bird Impact on Aircraft Structures Undergoing Large Deformations and Localised Failures

Numerical analyses of birdstrike were performed on aircraft light structures made up in metallic,... more Numerical analyses of birdstrike were performed on aircraft light structures made up in metallic, composite and polymeric materials, using the ESI/Pam-Crash solver code. The finite element models were developed calibrating the material models to take into account the different inelastic behaviours and failure modes. Three types of bird models were developed for the analyses, considering different combinations of porosity levels and shear strength of the bird materials. Adopting a Lagrangian approach featured with a numerical element elimination procedure, the computations were prosecuted also in presence of large distortions of the bird elements allowing to approximately analyse impacts with large deformations and perforations of the structures. The numerical-experimental correlations show that the developed finite element models were able to well represent the different failure mechanisms characterising the structural responses. The results also allow to evaluate how the severity of the load conditions experienced by the target in the numerical analyses depends on the porosity and the shear strength attributed to the bird material

Research paper thumbnail of Reliability of strain monitoring of composite structures via the use of optical fiber ribbon tapes for structural health monitoring purposes

Composite Structures, 2015

In aerospace industry, a lot of effort has been focused on the practical implementation of optica... more In aerospace industry, a lot of effort has been focused on the practical implementation of optical fibres on composite subcomponents for health monitoring purposes during the service life of an aircraft. To this direction the fibre optic ribbon tapes (FORTs) concept was developed in order to ease the handling, the surface placement and the maintenance of such sensitive sensors. In this paper, we investigate the structural durability of this concept comparing two ways of mounting the FORT (co-bonding and secondary bonding) under fatigue loading conditions. Through long term fatigue tests and utilizing additional experimental (electrical strain gauges (ESG)), theoretical as well as numerical tools, it is concluded that the deviation of the experimentally measured strains using the FORT approach versus conventional ESG values are well within an error of maximum 6%. Moreover, they remain in this error bound for as much as 10 6 loading cycles, rendering FORTs a reliable solution for aerospace SHM. In the final part of the study, the effect of the FORTs placement on the stiffness of a structure is assessed through numerical analysis of the changes of the dynamic characteristics as well as the modal response of an aeronautical subcomponent representative of a wing front spar.

Research paper thumbnail of Modelling competitive delamination and debonding phenomena in composite T-Joints

Procedia Engineering, 2011

Experimental studies on the failure mode of composite T-joint specimens, in the presence of adhes... more Experimental studies on the failure mode of composite T-joint specimens, in the presence of adhesive interlaminar layers, are presented. Tests underline the role played by the interaction between delamination and debonding phenomena. Quasi static analyses of the tests are performed by means of explicit FE models. A modelling technique based on a cohesive zone approach is adopted to simulate damage propagation both in the adhesive interface and in the most critical interlaminar layers of laminates. All the numerical results are compared against the experimental evidences in terms of fracture patterns, of load vs. displacement responses and local strain levels.

Research paper thumbnail of Morphing Composite Structures for Adaptive High Lift Devices

The work presents a design study for an aeronautical flap capable of smooth and progressive shape... more The work presents a design study for an aeronautical flap capable of smooth and progressive shape variations. Optimal configurations for takeoff and landing are taken from literature to define a reference design case and the corresponding loading conditions. An extraction mechanism to set the flap in optimal position is identified. Then, a morphing composite structure is devised to smoothly and progressively change the shape of the high lift device to enhance the functions and the versatility of such aerodynamic surface. An internal structure based on chiral auxetic cellular topology and a skin system supported by a corrugated composite panel are proposed. The technological processes for manufacturing such components are presented and discussed. A parameterized finite element model of the morphing flap is developed and structural analyses are carried out to investigate the feasibility of the morphing concept.

Research paper thumbnail of Numerical and Experimental Analyses of Multiple Delaminations in Curved Composite Laminates

Research paper thumbnail of Composite Corrugated Laminates for Morphing Applications

Morphing Wing Technologies

Research paper thumbnail of Design of a Leading Edge Morphing Based on Compliant Structures in the Framework of the CS2-AIRGREEN2 Project

Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation, and Control of Adaptive Systems; Integrated System Design and Implementation

This paper summarizes the results obtained in the framework of Clean Sky 2 REG-IADP, AIRGREEN on ... more This paper summarizes the results obtained in the framework of Clean Sky 2 REG-IADP, AIRGREEN on the development of a dedicated morphing device, i.e. a Leading Edge morphing. This device, designed so to be installed on a advanced, twin prop, regional aircraft, is conceived to guarantee high lift conditions together with a smoothed and continuous skin surface, especially important due to the presence of a laminar wing. The design of a such as complex devices required a multi-disciplinary approach, able to combine the aerodynamic performances and the structural ones related to the compliant structures concept adopted for the internal structure. The paper includes an overview of all the design challenges, the adopted solutions and finally the obtained numerical assessments.

Research paper thumbnail of A bi-phasic modelling approach for interlaminar and intralaminar damage in the matrix of composite laminates

Research paper thumbnail of Design and manufacturing of skins based on composite corrugated laminates for morphing aerodynamic surfaces

Smart Materials and Structures, 2017

Research paper thumbnail of Design of a morphing actuated aileron with chiral composite internal structure

Advances in aircraft and spacecraft science, 2014

The paper presents the development of numerical models referred to a morphing actuated aileron. T... more The paper presents the development of numerical models referred to a morphing actuated aileron. The structural solution adopted consists of an internal part made of a composite chiral honeycomb that bears a flexible skin with an adequate combination of flexural stiffness and in-plane compliance. The identification of such structural frame makes possible an investigation of different actuation concepts based on diffused and discrete actuators installed in the skin or in the skin-core connection. An efficient approach is presented for the development of aeroelastic condensed models of the aileron, which are used in sensitivity studies and optimization processes. The aerodynamic performances and the energy required to actuate the morphing surface are evaluated and the definition of a general energetic performance index makes also possible a comparison with a rigid aileron. The results show that the morphing system can exploit the fluid-structure interaction in order to reduce the actuation energy and to attain considerable variations in the lift coefficient of the airfoil.

Research paper thumbnail of Triggering system for the plastic collapse of a metal structural element

Research paper thumbnail of Carbon Fiber-Reinforced Smart Laminates with Embedded SMA Actuators---Part II: Numerical Models and Empirical Correlations

Journal of Materials Engineering and Performance, Apr 3, 2009

Up to now one of the main limits for a large use of shape memory alloys (SMA)-based smart composi... more Up to now one of the main limits for a large use of shape memory alloys (SMA)-based smart composite structures in the aerospace industry is the lack of useful numerical tools for design. Moreover, technological aspects still need a more detailed investigation. This paper shows how to overcome issues regarding embedding of NiTiNOL wires in carbon fibre/epoxy laminates. A crucial aspect of those structures is related to the load transfer capabilities between the SMA actuators and the host material during their activation. Embedding techniques developed for taking into account problems like thermal and electrical compatibility between actuators and host material and passive/active invasivity are reported in this paper. Simple smart laminates with several actuators were manufactured, tested, and deeply analyzed. In order to characterize the interface in the real operative conditions, pull-out tests were conducted on NiTiNOL wires embedded in composite fiber laminates. The results were compared to standard experiments on wires embedded in pure epoxy resin blocks.

Research paper thumbnail of Chiral-Rib Structures for Morphing Wings

Research paper thumbnail of Design of a Morphing Wing Using a Composite Chiral Structure

Research paper thumbnail of Composites Interlaminar Toughening Techniques by Means of Interleaved Nanofiber Veils: Experimental Evaluation

Research paper thumbnail of Modelling Technique to Optimise Energy Absorption in Helicopter Crashes

Research paper thumbnail of Evaluation of SLS-made PA 12 Under Uniaxial Tensile Test

The morphing structures provide a development in aero field applications and they are being a rea... more The morphing structures provide a development in aero field applications and they are being a realistic imitation of nature over time, bringing good efficiencies in many factors with respect to the conventional methodologies. On the other hand, these structures have some not-well predicted behaviors with new material applications. Polyamide 12 (PA12) is one of these new century materials manufactured by one of unconventional technologies, namely Selective Laser Sintering (SLS). Based on the morphing structures, the hexachiral and hexachiral tessellation morphologies are two of the in-demand researches not only in aero field but also in many other fields. As a sub-field of these researches, out-of-plane and in-plane crashworthiness of the hexachiral morphologies are being a great subject to be examined. Moreover, even there are many researches belong to out-of-plane crashworthiness, solely a limited number of resources for in-plane behavior can be found in literature. As a study case...

Research paper thumbnail of Tecniche di formatura di compositi con fibre vegetali e loro caratterizzazione

Research paper thumbnail of Optimisation of Energy Absorbing Subsystems for Helicopter Vertical Crashes

The experience gained in the last decades on the development of crashworthiness helicopter struct... more The experience gained in the last decades on the development of crashworthiness helicopter structures indicates that occupants’ protection can be achieved integrating different energy absorbing systems in landing gears, subfloor and seats. However, the mutual interactions between these different subsystems must be considered to achieve higher overall performances in case of crash events. This work proposes a numerical approach for the evaluation of the overall undercarriage performance, basing on an hybrid multi-body and finite element approach. A hybrid scheme of the subfloor lay-out is integrated with a multibody model of a crashworthy seat and an anthropomorphic dummy model. The modelling technique has been used to investigate and optimize the effects of local aspects on the overall crashworthy performances of the system such as the subfloor and the seat absorbing devices. Basing on the obtained results, the proposed methodology seems a promising approach to deal with the optimiz...

Research paper thumbnail of Development and Application of Numerical Approaches for Short Fibre Reiforced Ceramics

Topic: Structures and Materials) Ceramic matrix composites (CMC) have been extensively studied si... more Topic: Structures and Materials) Ceramic matrix composites (CMC) have been extensively studied since their discovery in the mid- seventies, particularly those made of silicon carbide (SiC) matrix with discontinuous carbon reinforcement. These materials are obtained by reinforcing a SiC matrix with bundles each made of hundreds or thousands of fibers. They present remarkably high toughness compared to traditional ceramics and have the potential of being used as structural materials in different fields, at temperatures up to about 1500°C. Present or potential applications include braking systems for aeromobiles and motor vehicles, spacecrafts, advanced engines, stationary gas turbines for power/steam co-generation, heat exchangers, heat treatment furnaces and components for nuclear reactors. A critical aspect is the necessity to evaluate, in terms of stiffness and strength, the expected material performance of structural elements made of CMC. In fact, traditional micromechanical appro...

Research paper thumbnail of Numerical Analyses of Bird Impact on Aircraft Structures Undergoing Large Deformations and Localised Failures

Numerical analyses of birdstrike were performed on aircraft light structures made up in metallic,... more Numerical analyses of birdstrike were performed on aircraft light structures made up in metallic, composite and polymeric materials, using the ESI/Pam-Crash solver code. The finite element models were developed calibrating the material models to take into account the different inelastic behaviours and failure modes. Three types of bird models were developed for the analyses, considering different combinations of porosity levels and shear strength of the bird materials. Adopting a Lagrangian approach featured with a numerical element elimination procedure, the computations were prosecuted also in presence of large distortions of the bird elements allowing to approximately analyse impacts with large deformations and perforations of the structures. The numerical-experimental correlations show that the developed finite element models were able to well represent the different failure mechanisms characterising the structural responses. The results also allow to evaluate how the severity of the load conditions experienced by the target in the numerical analyses depends on the porosity and the shear strength attributed to the bird material

Research paper thumbnail of Reliability of strain monitoring of composite structures via the use of optical fiber ribbon tapes for structural health monitoring purposes

Composite Structures, 2015

In aerospace industry, a lot of effort has been focused on the practical implementation of optica... more In aerospace industry, a lot of effort has been focused on the practical implementation of optical fibres on composite subcomponents for health monitoring purposes during the service life of an aircraft. To this direction the fibre optic ribbon tapes (FORTs) concept was developed in order to ease the handling, the surface placement and the maintenance of such sensitive sensors. In this paper, we investigate the structural durability of this concept comparing two ways of mounting the FORT (co-bonding and secondary bonding) under fatigue loading conditions. Through long term fatigue tests and utilizing additional experimental (electrical strain gauges (ESG)), theoretical as well as numerical tools, it is concluded that the deviation of the experimentally measured strains using the FORT approach versus conventional ESG values are well within an error of maximum 6%. Moreover, they remain in this error bound for as much as 10 6 loading cycles, rendering FORTs a reliable solution for aerospace SHM. In the final part of the study, the effect of the FORTs placement on the stiffness of a structure is assessed through numerical analysis of the changes of the dynamic characteristics as well as the modal response of an aeronautical subcomponent representative of a wing front spar.

Research paper thumbnail of Modelling competitive delamination and debonding phenomena in composite T-Joints

Procedia Engineering, 2011

Experimental studies on the failure mode of composite T-joint specimens, in the presence of adhes... more Experimental studies on the failure mode of composite T-joint specimens, in the presence of adhesive interlaminar layers, are presented. Tests underline the role played by the interaction between delamination and debonding phenomena. Quasi static analyses of the tests are performed by means of explicit FE models. A modelling technique based on a cohesive zone approach is adopted to simulate damage propagation both in the adhesive interface and in the most critical interlaminar layers of laminates. All the numerical results are compared against the experimental evidences in terms of fracture patterns, of load vs. displacement responses and local strain levels.

Research paper thumbnail of Morphing Composite Structures for Adaptive High Lift Devices

The work presents a design study for an aeronautical flap capable of smooth and progressive shape... more The work presents a design study for an aeronautical flap capable of smooth and progressive shape variations. Optimal configurations for takeoff and landing are taken from literature to define a reference design case and the corresponding loading conditions. An extraction mechanism to set the flap in optimal position is identified. Then, a morphing composite structure is devised to smoothly and progressively change the shape of the high lift device to enhance the functions and the versatility of such aerodynamic surface. An internal structure based on chiral auxetic cellular topology and a skin system supported by a corrugated composite panel are proposed. The technological processes for manufacturing such components are presented and discussed. A parameterized finite element model of the morphing flap is developed and structural analyses are carried out to investigate the feasibility of the morphing concept.

Research paper thumbnail of Numerical and Experimental Analyses of Multiple Delaminations in Curved Composite Laminates

Research paper thumbnail of Composite Corrugated Laminates for Morphing Applications

Morphing Wing Technologies

Research paper thumbnail of Design of a Leading Edge Morphing Based on Compliant Structures in the Framework of the CS2-AIRGREEN2 Project

Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation, and Control of Adaptive Systems; Integrated System Design and Implementation

This paper summarizes the results obtained in the framework of Clean Sky 2 REG-IADP, AIRGREEN on ... more This paper summarizes the results obtained in the framework of Clean Sky 2 REG-IADP, AIRGREEN on the development of a dedicated morphing device, i.e. a Leading Edge morphing. This device, designed so to be installed on a advanced, twin prop, regional aircraft, is conceived to guarantee high lift conditions together with a smoothed and continuous skin surface, especially important due to the presence of a laminar wing. The design of a such as complex devices required a multi-disciplinary approach, able to combine the aerodynamic performances and the structural ones related to the compliant structures concept adopted for the internal structure. The paper includes an overview of all the design challenges, the adopted solutions and finally the obtained numerical assessments.

Research paper thumbnail of A bi-phasic modelling approach for interlaminar and intralaminar damage in the matrix of composite laminates

Research paper thumbnail of Design and manufacturing of skins based on composite corrugated laminates for morphing aerodynamic surfaces

Smart Materials and Structures, 2017

Research paper thumbnail of Design of a morphing actuated aileron with chiral composite internal structure

Advances in aircraft and spacecraft science, 2014

The paper presents the development of numerical models referred to a morphing actuated aileron. T... more The paper presents the development of numerical models referred to a morphing actuated aileron. The structural solution adopted consists of an internal part made of a composite chiral honeycomb that bears a flexible skin with an adequate combination of flexural stiffness and in-plane compliance. The identification of such structural frame makes possible an investigation of different actuation concepts based on diffused and discrete actuators installed in the skin or in the skin-core connection. An efficient approach is presented for the development of aeroelastic condensed models of the aileron, which are used in sensitivity studies and optimization processes. The aerodynamic performances and the energy required to actuate the morphing surface are evaluated and the definition of a general energetic performance index makes also possible a comparison with a rigid aileron. The results show that the morphing system can exploit the fluid-structure interaction in order to reduce the actuation energy and to attain considerable variations in the lift coefficient of the airfoil.

Research paper thumbnail of Triggering system for the plastic collapse of a metal structural element

Research paper thumbnail of Carbon Fiber-Reinforced Smart Laminates with Embedded SMA Actuators---Part II: Numerical Models and Empirical Correlations

Journal of Materials Engineering and Performance, Apr 3, 2009

Up to now one of the main limits for a large use of shape memory alloys (SMA)-based smart composi... more Up to now one of the main limits for a large use of shape memory alloys (SMA)-based smart composite structures in the aerospace industry is the lack of useful numerical tools for design. Moreover, technological aspects still need a more detailed investigation. This paper shows how to overcome issues regarding embedding of NiTiNOL wires in carbon fibre/epoxy laminates. A crucial aspect of those structures is related to the load transfer capabilities between the SMA actuators and the host material during their activation. Embedding techniques developed for taking into account problems like thermal and electrical compatibility between actuators and host material and passive/active invasivity are reported in this paper. Simple smart laminates with several actuators were manufactured, tested, and deeply analyzed. In order to characterize the interface in the real operative conditions, pull-out tests were conducted on NiTiNOL wires embedded in composite fiber laminates. The results were compared to standard experiments on wires embedded in pure epoxy resin blocks.